VIP and hydrops fetalis: Mechanisms of HF IP (these two IP areas are slightly different) are thought to downregulate the expression of MHC I and β2-microglobulin (84), and the secretion of immunosuppressive cytokines and neuropeptides (“IP guardians”) such as TGF-β1/2, IL-10, alpha-melanocyte-stimulating hormone (α-MSH), calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP) (85–87).